1. Field of the Invention
The invention is directed to an acid bath for the galvanic deposition of bright, ductile and smooth copper coats and to the use of this combination. The bath according to the invention can be used for strengthening the conductors of printed circuits as well as for decorative applications.
2. Description of the Prior Art
The addition of organic substances to galvanic copper baths to achieve bright depositions has been known for a long time. However, the numerous compounds which are already known for this purpose, e.g. thiourea, gelatins, molasses, coffee extract, "basic" dyestuffs and thiophosphoric acid esters, no longer have any practical significance, since the quality of the copper coats obtained by their use--in particular with respect to homogeneous appearance, hardness and breaking elongation--do not meet current requirements.
Baths containing a mixture of high-molecular compounds containing oxygen with organic, especially aromatic, thio compounds are known from the prior art (DE-AS 1521062). However, these baths yield unsatisfactory results with respect to control of metal and/or levelling or smoothing.
By way of improvement, DE-AS 2039831 describes an acid copper bath containing at least one dye from the polymeric phenazonium compound series in addition to a polymeric oxygen-containing compound and a thio compound with a water-soluble group. Other efforts describe the combination of organic thio compounds and polymeric oxygen-containing compounds with other dyes such as Crystal Violet (EP-PS 71512) or phthalocyanine derivatives with aposafranene (DE-PS 3420999) or a combination with amides (DE-PS 2746938).
A disadvantage in the use of conventional oxygen-containing high-molecular compounds is the stability in the electrolyte. In normal use, these compounds slowly decompose during the electrolysis into water-insoluble polymers which continue to build up in the electrolyte, form a jelly-like border around the walls, and are finally deposited on the goods themselves so that these goods are marred by defects which render them unusable. This decomposition is extremely intensified when the bath temperature rises above 28.degree. C.